The present invention relates to releasable tool fastening systems to tools for use with them.
Saber saws are reciprocating power saws that are often used for work to break things off and for rough cutting applications, and it is known in the prior art in such saws to use a fast-change blade clamping system, so that when necessary, a blade can be changed quickly and easily. In known blade clamping arrangements, an interaction as a rule occurs between curved faces, ball bearings, and inclined planes for firmly clamping a standard saw blade shaft. As a rule, the blade is firmly held by the engagement of a peg bearing or ball bearing with a through hole embodied in the blade shaft, to counteract longitudinal stresses when the flat surface of the blade shaft is firmly clamped. Although these known systems work to restrict one degree of freedom of a saw blade, as a rule they are based on the mechanical attachment of the blade in a slot in the fastening mechanism, in order to restrict the remaining degrees of freedom, and this is highly dependent on the production tolerances that can be attained. In practice with these known systems, a certain degree of undesired play of the blade then occurs.
In one aspect of the present invention, a tool fastening mechanism having the following elements is furnished: a housing, which has a clamping opening for receiving the shaft of a tool to be fastened, wherein the clamping opening tapers downward in a first direction, in which in use a tool shaft is introduced into the clamping opening, and which also tapers in a second direction extending perpendicular to the first direction, having an opening in the housing which intersects the clamping opening, and having a locking pin, which is movable in the opening between a first position, in which it is retracted from the clamping opening, so that in use it allows a tool shaft to be introduced into and removed from the clamping opening, and a second position, in which it protrudes into the clamping opening, so that in use it takes the tool shaft into engagement, in order to prevent the shaft from being pulled out of the opening, and wherein upon introduction of a tool shaft into the opening in use, the tapering of the opening in the first direction restricts a motion of the shaft in a third direction extending perpendicular to the first and second directions; this tapering of the opening in the second direction lends the shaft an engagement action and presses it against one side of the opening, in order to restrict a motion in the second direction, and engagement of the locking pin with the shaft restricts a motion in the first direction, as a result of which all six degrees of freedom of the tool shaft are restricted.
The present invention also furnishes a tool for use with a fastening mechanism of the invention, which has a shaft whose sides taper inward toward the clamping end and also has an engagement face, embodied on the tapering shaft part, which face is engaged in use by a locking pin of the fastening mechanism.
A system comprising a tool fastening mechanism and a tool for use with it has the advantage that the system, because of the fact that the converging sides of the clamping opening are inclined in the transverse plane to one another, creating a double taper in the opening, counteracts all six degrees of freedom of an introduced blade within the production tolerances that are attainable by conventional mass-production methods that are used in systems of the prior art, which as explained above are not capable of completely restricting the tool without excessive mechanical play. If the taper of the clamping opening extends symmetrically, the system furthermore permits bidirectional fastening, so that a tool, such as a saber saw blade, can be secured with the teeth pointing either upward or downward, thus enhancing the versatility of the tool, and the disposition of the locking pin makes it possible to load a tool into the clamping device without first having to maneuver the tool over fixed positioning pins, thus making it simpler to use. The frictional engagement of the locking pin also means that the only imaginable way in which a tool could be released by mistake from the saw during use would be a sudden complete failure of the fastening mechanism or of the tool shaft.
Moreover, the embodiment of the tool shaft, in comparison with that known from the prior art, enables improved strength, and the increased torsional and flexural strength that is thus possible in the shaft allows narrower cutting radii. In particular, because of the tapering design of the clamping opening and of the tool shaft, the tool cross section is maximized at the place where it meets the tool body, which in use is equivalent to the region of maximum bending stress, thus improving the overall strength of the blade in comparison to the prior art versions. In the prior art versions, a graduated change of cross section has been necessary as a rule at the transition between the tool shaft and the tool body, which increases the likelihood of a fatigue fracture caused by stress concentrations at the change in cross section.
Preferably a hole is embodied in the tool shaft, and the locking pin extends through it, to prevent the tool shaft from being pulled out of the clamping opening; the front edge of the hole forms the locking pin engagement face of the tool shaft. This has the advantage that the compulsory longitudinal force can be applied to the tool shaft in a balanced way, so that the shaft can be rotated in proper engagement with the clamping opening. As an alternative to this, the tool shaft could be embodied in at least one side of it with a notch or a recess, with the notch having a side face where the pin can engage it, to prevent the shaft from thus being pulled out of the clamping opening.
In the preferred embodiment, the locking pin has a tapering portion, which cooperates with the front edge of the hole or with the side notch in the introduced tool shaft in such a way that as the locking pin is pressed further into the clamping opening, the engagement action resulting from the taper on the locking pin draws the shaft deeper into the clamping opening. This has the advantage that the tool can be clamped very firmly in the opening, without the user having to exert excessive force by the tool itself, which for fragile tools such as saw blades could cause them to break. The cone angle of the tapering portion of the locking pin is preferably less than tanxe2x88x921 (2xcexc), and xcexc is equal to the coefficient of static friction for the specified contact faces, which assures that the locking pin by frictional engagement acts counter to stresses exerted along the axis of the tool part.
In the preferred embodiment, action is exerted on the locking pin by a prestressing means, which moves it into the clamping opening with sufficient force to assure that the engagement action between the tapering part of the locking pin and the blade shaft brings about proper fastening of the tool. Once the locking pin is engaged, it is effectively held firmly by static friction, so that the prestressing means cannot be overcome by stresses exerted on the blade. A release mechanism is then provided, which is activated by the user in order to retract the locking pin from the opening, counter to the stress exerted by the prestressing means, in order to release a tool secured in the mechanism. This can be achieved especially effectively whenever the end of the locking pin remote from the opening is connected to a release lever, which is mounted pivotably on the housing, so that the pivoting of the release lever effects a motion of the locking pin between its first and second positions. The prestressing means can then be embodied as a torsion spring, which is in engagement with the release lever and presses it into a position in which the lever presses the locking pin into the clamping opening. This has the advantage that an especially simple yet effective retaining and release system for the locking pin is thus furnished.
The mechanism furthermore advantageously includes a blade ejection system, in the form of a carriage, which is mounted in the clamping opening for executing a limited longitudinal displacement therein and is prestressed toward the orifice of the opening, for instance by a compression spring, so that the tip upon introduction of a shaft into the opening takes the carriage into engagement and pushes it toward the rear part of the opening, counter to the stress from the compression spring. Upon release of the shaft from the opening by actuation of the release lever, the compression spring then pushes the carriage toward the front, as a result of which the shaft is pushed out of the orifice of the opening. The forward position of the carriage is preferably then disposed such that it is located above the intersection between the locking pin opening and the clamping opening; the locking pin, on its front edge toward the carriage, is provided with cutouts that enter into engagement with a V-shaped notch in the carriage, to assure a proper engagement between the two parts. In this way, when the tool is pulled out of the opening, the mechanism automatically locks the locking pin in its first position, thus allowing a new tool to be introduced without the user having to use the release lever to release the locking pin from the clamping opening. This makes it possible to load a tool into the mechanism and remove it again with only one hand, which is especially advantageous, since it enables a user to remove a hot tool part without the risk of burning himself.
Preferably, the hole in the shaft of the tool is oblong in its introduction direction into the clamping opening, in order to take appropriate account of the various thicknesses of the locking pin, because of the tapering portion embodied on it. This has the advantage that the locking pin can be moved forward without reducing the cross-sectional area of the tool shaft. Moreover, the cross-sectional area of the locking pin can be increased without excessively weakening the tool shaft.
It is also especially advantageous if three protrusions are embodied on the converging sides of the tool shaft, at least one of which is provided on each of the two sides. This has the advantage that because of the resultant contact between the tool shaft and the sides of the opening, it is assured that the reaction forces exerted will be determined statically, creating an especially stable fastening of the shaft without play, and this fastening itself takes appropriate account of normal production tolerances. As an alternative, the protrusions can be provided on the converging walls of the clamping opening, instead of on the sides of the shaft, to obtain the same statically determined reaction forces, although the production of the resultant mechanism will be more expensive, and a bidirectional fastening might not be possible.
For good comprehension of the invention, several exemplary embodiments of the invention will now be described in conjunction with the accompanying drawings.